Which of the following best describes the musical developments in early 14th-century France?

The early 14th century in France marked a vital period in music history characterized by significant advancements, particularly in rhythm, meter, and harmony. This era saw the emergence of new musical techniques that allowed composers to explore varying tempos and complex rhythms, which were essential in the development of what would later become more defined forms of polyphony.

Composers began to experiment with different meters, creating music that was more dynamic and expressive. Furthermore, this time period introduced the use of different harmonic structures, providing a richer texture to the music. The innovations in these areas paved the way for later developments in Renaissance music, where these advancements in rhythmic and harmonic language became fundamental.

The other options do not accurately reflect the notable developments occurring during this period. For instance, while sacred themes continued to be important, the era was notable for both sacred and secular works. The complexity of music actually increased, rather than decreased, as composers embraced more sophisticated musical structures. Additionally, while much vocal music was produced, there was also a growing interest in instrumental music, which began to emerge in this time frame. Thus, option C accurately captures the essence of musical developments in early 14th-century France.